Method and device for cooling ultrasonic transducers

ABSTRACT

The invention relates to a method and a device for cooling ultrasonic transducers. The inventive device is characterised in that it consists of at least one piezo stack ( 4 ) and at least two cylindrical transducer bodies ( 5 ), which together with the piezo stack ( 4 ) form an λ/2 oscillator. In multiple transducer assemblies, two respective transducer bodies ( 5 ) can be combined to form a common transducer body ( 6 ) and the transducer bodies ( 5, 6 ) comprise flow channels ( 7 ), through which pressurised coolant can flow. The inventive method for cooling ultrasonic transducers is characterised in that the body of the ultrasonic transducer is traversed and/or surrounded by a pressurised coolant. This enables the heat that is generated in the transducers to be directly dissipated by convection. In addition the inventive elements enable the creation of a large common contact surface between the transducers and the coolant. The heat dissipation achieved is substantially more effective than in known methods and the inventive elements thus guarantee a high-performance continuous operation.

The invention relates to a method and a device for cooling ultrasonictransducers with the features recited in the preambles of claim 1.

During the operation of ultrasonic transducers, power losses areconverted into heat. These losses are caused, on one hand, by electricallosses and, on the other hand, by internal friction in the piezoelements produced when electric energy is converted into mechanicalenergy. Different methods are generally known to efficiently remove thegenerated heat. Conventional cooling systems are based on heat transferby thermal conduction or convection. In most cases, a combination ofthese two operating principles is employed.

High-power ultrasonic transducers, which inherently have a largeoscillation amplitude, are difficult to cool, because large quantitiesof heat must be removed without generating more friction or additionalheat. Thus far, only gaseous media have been used successfully toefficiently remove heat by convection, because cooling fluids tend togenerate substantial quantities of additional energy due to cavitations,potentially damaging the transducer. Large quantities of gas athigh-pressure are required when with gas, which makes this coolingmethod quite uneconomical. Moreover, the cooling gas must be free ofsolid or liquid contaminants to prevent short-circuits caused by theformation of bridge circuits at the high voltages at which thehigh-power ultrasonic transducers operate.

EP 0553804 A2 discloses a cooling system for a high-frequency ultrasonicconverter based on thermal conduction. A heat sink is arranged behindthe ultrasonic converter and connected with the housing by aheat-conducting resin. The heat is initially transmitted from thetransducer to the heat sink and from there via the resin to surroundinghousing, from where the heat is carried away by the ambient air. Thistype of cooling is inadequate for high-power devices and cannot be usedat large oscillation amplitudes of several micrometers, because a largeamount of energy is then transferred to the resin.

In many cases, the cooling systems for ultrasonic converters operateexclusively by removing heat by convection through openings disposed ina housing surrounding the transducer (e.g., SONOPULS HD 60, BANDELINelectronic GmbH & Co. KG). This type of cooling is also inadequate forhigh-power applications.

Several modifications of such cooling systems are known, with additionalcooling provided by fans or compressed air. With this type of cooling,substantial quantities of dust or moisture can disadvantageously betransported into the housing, which increases the danger of electricshort-circuit due to the formation of bridge circuits by electricallyconducting contaminants. Also known are closed systems with a fan andheat exchange from the inside to the outside. These systems are alsoquite complex and only allow limited heat removal.

EP 0782125 A2 discloses an arrangement for cooling a high-frequencyultrasonic transducer, whereby a heat-conducting pipe carrying a liquidis connected with a heat sink arranged downstream of the transducer. Thecooling fluid is supplied and removed via connecting lines. The heat isthus removed from the heat sink by convection. In a particularembodiment of this cooling system, the heat-conducting pipe is entirelyor partially formed as a channel in the material surrounding thetransducer for obtaining a particularly large contact surface. Thecooling fluid does not flow through the ultrasonic transducer, butrather flows through a cooling system that is in contact with thetransducer. This arrangement, too, is inadequate for efficient heatremoval from high-power devices.

WO 0008630 A1 discloses an arrangement for removing heat, in particularfrom ultrasonic transducers operating at high power. Heat removal isbased on a combination of thermal conduction and convection. The surfaceof the transducer body is provided with a vibration-absorbing layer,which reduces mechanical friction losses during heat transfer. A layerof heat conducting material is disposed above the vibration-absorbinglayer. A heat sink, from which the heat can be removed by cooling meansthrough convection, is arranged on the heat conducting layer. Thisarrangement has the disadvantage that the temperature gradients at thetransitions between layers reduce the efficiency of heat removal.Moreover, the maximum common contact surface between the transducer andthe cooling device is limited to the transducer surface. Ultrasonictransducers can therefore operate continuously at high power only whenlarge quantities of cooling fluid are supplied, which makes the methodquite uneconomical.

U.S. Pat. No. 5,936,163 discloses an ultrasonic transducer, which isused in high temperature environments, such as reactors and steam pipes.For removing heat introduced into the transducer from the surroundings,the body of the ultrasonic transducer is cooled by a circulating coolingmedium.

All these known solutions tend to prevent ultrasonic transducers fromoperating continuously at high power levels and/or tend to allowcontinuous operation only with diminished efficiency.

It is therefore an object of the invention to provide a method and adevice for cooling ultrasonic transducers, which remove the heatgenerated by thermal losses more effectively than previously knowndevices and which therefore enable ultrasonic transducers to reliablyand economically operate continuously even at high power levels.

The object is solved by the invention by a method having the featuresrecited in claim 1. The method according to the invention for coolingultrasonic converters is characterized in that a cooling fluid flowsthrough and/or around the body of the ultrasonic transducer. In thisway, the heat generated in the transducers is advantageously removeddirectly through convection. No thermal conduction via heat sinks isrequired. The flow through the transducer provides a large commoncontact surface between the converters and the cooling fluid. The heatis much more effectively removed than with conventional methods, withthe means according to the invention therefore allowing ultrasonictransducers to operate continuously at high power levels.

Advantageously, within the context of the present method, the pressureof the cooling fluid is dimensioned so as to reduce or preventcavitations.

Preferably, the pressure is set in a range from 2 to 20 bar, preferably5 bar. This approach significantly reduces the risk of damaging thedevice through cavitations and reduces or even prevents cavitationswhich can introduce additional energy.

The pressure of the cooling fluid can be generated by suitablydimensioning the flow-through channels and/or by a gas pressure.

Moreover, in the context of the method of the invention, the flowthrough the body of the ultrasonic transducer is provided from theinterior region to the exterior region, whereby fluid pressure is builtup in the interior region and cooling fluid is drained via the housing,or from the exterior region to the interior region, wherein pressure isbuilt up in the exterior region and the cooling fluid is drained via theinterior region. This method is removes heat from the transducers withparticular efficiency. In addition, to eliminate cavitations, pressuremay be established in both the interior region and the exterior region,whereby a pressure gradient must be established between the interiorregion and the exterior region to allow cooling fluid flow.

In addition, cooling fluid can flow around the body of the ultrasonictransducer preferably in the interior region and/or in the exteriorregion, because heat is thereby removed from the transducer surface byconvection.

The interior region is herein defined as the hollow space between thetensioning rod and the transducer body, whereas the outer region isdefined as the space between the transducer body and the housing.

Moreover, in the context of the method of the invention, the coolingfluid may be an electrically non-conducting fluid to prevent electricshort-circuits.

The device according to the invention for cooling ultrasonic transducersadvantageously includes at least one piezo stack and at least twocylindrical transducer bodies which together with the piezo stack form aλ/2 oscillator, wherein assemblies with multiple transducers can beformed by combining two transducer bodies to a unitary transducer body,and wherein at least one of the at least two transducer bodies includesat least one flow-through channel, through which cooling fluidintroduced under pressure can flow. In this way, the heat generated inthe transducers can advantageously be removed directly by convection. Noheat conduction via heat sinks is required. Moreover, with the meansaccording to the invention, a large common contact surface between thetransducers and cooling fluid can be realized. This form of heat removalis significantly more effective than conventional methods, so that themeans of the invention enable continuous operation of ultrasonictransducers operating at high power levels.

According to an advantageous embodiment of the invention, the pressureof the cooling fluid is dimensioned so as to reduce or even preventcavitations. Preferably, the pressure is adjusted in a range from 2 to20 bar, most preferably the pressure is 5 bar. Advantageously, thisapproach significantly reduces the risk of damage to the device throughcavitations and reduces or prevents the introduction of additionalenergy generated by cavitations.

Moreover, according to advantageous embodiment of the invention, atleast one flow-through channel is formed as a slit, which provides aparticularly large common contact surface between the transducer bodyand cooling fluid, increasing the heat removal efficiency.

According to another advantageous embodiment of the invention, thedevice includes a tensioning rod arranged in a hollow space of the atleast two transducer bodies and having at least two openings and atleast one guide channel, through which the pressurized cooling fluidintroduced can flow. The cooling fluid can thereby be introduced intothe hollow space in a particularly simple and uniform manner.

In addition, according to another advantageous embodiment of theinvention, the cooling fluid can be supplied via the at least one guidechannel and removed via the at least one flow-through channel.Preferably, the cooling fluid can also be supplied via the at least oneflow-through channel and removed via the at least one guide channeldisposed in the tensioning rod. In this way, cooling fluid can flow in aparticularly straightforward manner through the transducer body from theinterior region to the exterior region, or for the exterior region tothe interior region.

In addition, according to an advantageous embodiment of the invention,the device includes a fluid-tight housing. The housing is provided, onone hand, for protecting the active elements of the transducer and, onthe other hand, represents a particularly advantageous option forreceiving and guiding the cooling fluid.

In addition, according to an advantageous embodiment of the invention,the device includes a flange which is connected with the housing and/orwith a horn and/or with an end mass. The flange facilitates attachingthe housing. Moreover, the horn is a particularly advantageous optionfor providing a connection with a sonotrode.

According to another advantageous embodiment of the invention, thedevice includes at least one connection for a cooling fluid line,through which the cooling fluid can flow into and/or can be removed fromthe hollow space of the transducer bodies. In this way, the hollow spacecan be easily connected with a cooling fluid supply device and readilysupplied with cooling fluid.

According to an advantageous embodiment of the invention, the device hasat least one connection for a cooling fluid line, through which thecooling fluid can flow into the at least one guide channel and/or can beremoved from the at least one guide channel. In this way, the guidechannel can be easily connected with a cooling fluid supply device andreadily supplied with cooling fluid.

According to yet another advantageous embodiment of the invention, thedevice has at least one connection for a cooling fluid line, throughwhich the cooling fluid can flow into the housing and/or can be removedfrom the housing. In this way, the housing can be easily connected witha cooling fluid supply device and readily supplied with cooling fluid.

Finally, according to still another advantageous embodiment of theinvention, the cooling fluid can flow at least partially around theinner surface and/or at least partially around the outer surface of atleast one of the at least two transducer bodies. In this way, heat iseffectively removed from the transducer bodies by convection.

According to another embodiment of the invention, the transducer bodiesdo not include flow-through channels. In this embodiment, the coolingfluid only flows around the transducer bodies, with the interior spacebeing connected to the exterior space by a connecting channel.

Additional advantageous embodiments of the invention include featuresrecited in the other dependent claims.

Embodiments of the invention will be described hereinafter withreference to the related drawings. It is shown in:

FIG. 1 a schematic cross-sectional view of an ultrasonic transducer witha cooling device having an axially arranged supply line for the coolingfluid;

FIG. 2 a schematic cross-sectional view of an ultrasonic transducer witha cooling device having two radially arranged supply lines for thecooling fluid; and

FIG. 3 a schematic cross-sectional view of an ultrasonic transducer witha cooling device without flow-through channels, and with a connectingchannel.

FIG. 1 shows schematically a longitudinal cross-section of an ultrasonictransducer, which includes an embodiment of the device according to theinvention for cooling the ultrasonic transducer. The ultrasonictransducer is constructed of cylindrical transducer bodies 5, 6 andpiezo stacks 4 which are arranged between the end faces of correspondingtransducer bodies 5, 6. Several of the transducer bodies 5, 6 areconfigured as unitary transducer bodies 6, wherein a respective piezostack 4 is arranged on each of the end faces. A respective one of thepiezo stacks 4 in conjunction with one of the transducer bodies 5 andwith either one half of one of the unitary transducer bodies 6 or withone half of two unitary transducer bodies 6 forms a λ/2 oscillator. Thetransducer bodies 5, 6 have flow-through channels 7 extending in theradial direction. The transducer bodies 5, 6 and piezo stacks 4 arealternatingly arranged on a tensioning rod 3 having terminal threads.This arrangement is secured and tensioned with two threaded end masses10 which are arranged on opposite sides of the tensioning rod 3, witheach of the end masses 10 being screwed on to a terminal thread of thetensioning rod 3. The tensioning rod 3 includes a guide channel 13 forcooling fluid. A connection for a cooling fluid line 1, which forms thesupply line 1 for the cooling fluid, is provided on one end of the guidechannel 13. The tensioning rod has an exit opening for the cooling fluidthat flows out of the guide channel into the hollow space 11 of thetransducer bodies. The opposite end mass 10 is connected with a horn 8capable of connecting to a sonotrode and transmitting the mechanicaloscillations generated by the transducer. The device is provided with afluid-tight housing 12 for receiving the cooling fluid, which isconnected with a flange 9 for installation in an external system. Theflange 9 is connected with the horn 8. The flange has a connection for acooling fluid line 2, which forms the drain line 2 for the cooling fluidfrom the housing 12. The cooling fluid line for the supply 1 runsthrough the housing 12. The cooling fluid is introduced under pressureinto the guide channel 13 of the tensioning rod 3 through the supplyline 1. The cooling fluid is supplied into the hollow space 11 of thetransducer bodies through the guide channel 13. The cooling fluid thenflows through the transducer bodies and finally through the flow-throughchannels 7 of the transducer bodies 5, 6. The heat generated by thetransducers is thereby directly transferred to the cooling fluid throughconvection. The cooling fluid exiting from the flow-through channels 7is collected in the housing 12 and removed from the device through thedrain 2. In this way, the ultrasonic transducer can be cooled moreeffectively than with conventional methods. The means of the inventionalso enable continuous operation of ultrasonic transducers at high powerlevels.

The lifetime of the transducer bodies can be increased and/or the flowthrough the slit-like flow-through channels 7 can be improved byproviding openings, for example circular bores, on the ends of theflow-through channels 7. Advantageously, the diameter of the bores isgreater than the width of the slits.

FIG. 2 shows schematically a longitudinal cross-section of the design ofan ultrasonic transducer with another embodiment of the device of theinvention for cooling the ultrasonic transducer, which essentiallycorresponds to the device depicted in FIG. 1. However, unlike theembodiment of FIG. 1, two supply lines 1 for the cooling fluid areprovided, which each extend radially from the outside through thehousing 12 and the end masses 10 into the hollow space 11 between thetensioning rod 3 and the transducer bodies 5, 6. The connections 1 thatconnect the cooling fluid lines to the hollow space 11 are here disposedon the opposite ends of the transducer. The cooling fluid is thenintroduced under pressure into the hollow space 11 from the oppositeends and removed through the flow-through channels 7. This arrangementadvantageously removes heat more uniformly over the entire length of thedevice than the arrangement of FIG. 1. Accordingly, the ultrasonictransducer is cooled more effectively than with the embodiment depictedin FIG. 1.

FIG. 3 shows another embodiment of the invention, wherein the transducerbodies 5, 6 lack flow-through channels 7. However, the interior space 11is connected to the exterior space 14 by a connecting channel 15.

In a first variant, the cooling fluid is supplied through the supplyline 1, reaches the interior space 11 via the guide channel 13, flowsaround the transducer bodies 5, 6, cooling them, then exits the interiorspace 11 through the connecting channel 15, and is removed via theexterior space 14 and the drain line 2. In this variant, only the insideof the transducer bodies 5, 6 is cooled.

Alternatively, in a second variant, only the outside of the transducerbodies 5, 6 can be cooled, by supplying cooling fluid through thehousing supply line 1 a and a circular line 17. The cooling fluidsupplied through the housing supply line 1 a is uniformly supplied anddistributed by the circular line 17, and flows around the outside of thetransducers 5, 6, and forms at least here a cooling fluid layer, beforebeing removed through the drain 2.

In a third variant, both the interior surfaces and the exterior surfacesof the transducer bodies 5, 6 can be cooled by supplying cooling meansinto the interior space 11 through the supply line 1, and also into theexterior space 14 through the housing supply line 1 a.

The cooling means supplied through the supply line 1 for cooling theinterior surfaces and through the housing supply 1 a for cooling theexterior surfaces of the transducer elements 5, 6 are removed throughthe drain line 2.

Cavitations can be prevented with the present embodiment by generatingin the housing 12 a gas pressure, in the present embodiment 6 bar, viathe gas pressure connection 6.

The invention is not limited to the illustrated embodiments andmodifications. Additional embodiments and modifications can be realizedby combining the aforedescribed means and features, without departingfrom the scope and spirit of the invention.

LIST OF REFERENCE SYMBOLS

-   -   1 connection for cooling fluid lines, supply line    -   1 a housing supply line    -   2 connection for cooling fluid lines, drain    -   3 tensioning rod    -   4 piezo stack    -   5 transducer body    -   6 unitary transducer body    -   7 flow-through channel    -   8 horn    -   9 flange    -   10 end mass    -   11 hollow space, interior space    -   12 fluid-tight housing    -   13 guide channel    -   14 exterior space    -   15 connecting channel    -   16 gas pressure connection    -   17 circular line

1. Device for cooling ultrasonic transducers, comprising at least onepiezo stack (4) and at least two cylindrical transducer bodies (5),which together with the piezo stack (4) form a λ/2 oscillator, whereintwo corresponding transducer bodies can be combined as multipletransducer arrangements to form a unitary transducer body (6),characterized in that the transducer bodies (5, 6) are surrounded by aninterior space (11) and an exterior space (14), and that at least one ofthe at least two transducer bodies (5,6) includes at least oneflow-through channel (7), through which a cooling liquid introducedunder pressure can flow, and/or that at least one connecting channel(15) is arranged between the interior space (11) and the exterior space(14), wherein the cooling liquid flows directly through the transducerbodies (5, 6) through the flow-through channel (7) and/or directlyaround the transducer bodies (5,6) through the interior space (11),wherein at least one flow-through channel (7) is formed as a slit andwherein the device further comprises a tensioning rod (3) arranged in ahollow space (11) formed by at least two transducer bodies (5, 6) andhaving at least one opening and at least one guide channel (13), throughwhich the cooling liquid introduced under pressure can flow, and whereinthe device is equipped in such a manner that the cooling liquid can besupplied through the at least one guide channel (13) and removed throughthe at least one flow-through channel (7), and that the cooling liquidcan be supplied through the at least one flow-through channel (7) andremoved through the at least one guide channel (13) disposed in thetensioning rod (3).
 2. Device according to claim 1, characterized inthat the pressure is dimensioned so as to reduce or prevent cavitations,and that the pressure is adjusted in a range from 2 to 20 bar, andpreferably is 5 bar.
 3. Device according to claim 1, characterized inthat the device includes a liquid-tight housing (12) and a flange, whichis connected with the housing (12) and with a horn (8), and that thedevice includes at least one corresponding connection (1, 2) for acooling liquid through which the cooling liquid can flow into the hollowspace (11) and/or be removed from the hollow space (11), or that thedevice includes at least one corresponding connection (1, 2) for acooling liquid line, through which the cooling liquid can flow into theat least one guide channel (13) and/or be removed from the at least oneguide channel (13), or that the device includes at least onecorresponding connection (1 a,2) for a cooling fluid line, through whichthe cooling fluid can flow into the housing (12) and/or be removed fromthe housing (12).
 4. Device according to claim 1, characterized in thatthe cooling liquid can flow at least around a portion of the innersurface and/or at least around a portion of the outer surface of atleast one of the at least two transducer bodies (5, 6).
 5. Deviceaccording to claim 1, characterized in that openings are disposed on theends of the flow-through channels (7), which openings have a diameterthat is greater than the width of the flow-through channels (7).